I guess the added occlusion can have an effect - particularly if the point of view is close to the ground. I've never tested it. But I'd expect it to be much smaller (if measurable at all) than extending the range for ground clutter (and thus inflating the number of billboards proportional to the square of the range increase).

Even uncooled thermal cameras would be a substantial benefit. That being said, thermal cameras are actually one of my favourite examples where export control actually worked for decades. You fully comprehend their value only after you've actually seen it. For a long time the Soviets simply believed that it was just a "marginally better" version of the IR sights that they had and knew.
Also, there's a substantial cost difference between what's commercially available (like a 160x120 pixel resolution uncooled thermal camera that you can have for about two grand) and military grade cameras that offer 30 frames per second or better, and at least four times the resolution, which still are export restricted (therefore, availability may be a greater issue for users of Russian legacy tanks than the price itself). The question is how many other nations outside of NATO actually have the necessary manufacturing capacity. Russian tank models with thermals got them delivered from France (Thales), as far as I know. That indicates that there still is no indigeneous production line (and maybe won't be, as long as non-NATO countries respect patents that may protect the companies that developed those camera systems). Non-WTO states like North Korea may have no qualms about stealing the technology, but their priorities may lie elsewhere.
Just saying, there may be more to it than sheer stupidity.

Active Protection Systems could substantially increase their battlefield life expectancy. Provided that your lawyer brigade isn't concerned about the prospect of getting sued by anyone who may be around during an intercept.

There are many factors at play beyond visual scene complexity, like the integration of the render cycle with the simulation cycle, and possible interdependencies. As a minimum you need to guarantee that ANY scene you would throw at the graphics card is guaranteed to render at 90 frames per second. The next big - and largely unsolved - problem is that of movement within the virtual environment. What works with first person shooters doesn't work - at all, as far as I can see - with VR games. So, this may require an entirely different approach to the whole design of the game.
It's these points that make a direct transfer of an existing title into a VR title such a big challenge. I'm not saying "insurmountable" - but the complexity is by far greater than just looking at the polycount of a scene. Just because one can imagine that a solution exists doesn't mean that it's easy to get there.

It doesn't update in real life either, not even with a battlefield management system.
Our map already shows more information than you'd normally have. If at all, I'd rather increase map update intervals.
This is the whole point of Steel Beasts, and one that most games get wrong - you never have complete information about what's going on in battle, and yet you must make decisions (indecision being one of your options, often not the best one). You can only try to mentally add the missing pieces - by using the 3D view in addition to the map, by thinking in terms of doctrinal behavior of the enemy, and force templates.